With conventional single fiber ferrules that are used in industry standard connectors such as SC, FC and ST.RTM. connectors, lateral alignment of the end faces of the ferrules is accomplished by use of an alignment sleeve into which two opposed cylindrical ferrules are inserted and aligned. Because there is a single fiber located concentric to the outer diameter of the ferrule, the relative rotational alignment of the two opposed end faces is not as critical. In such connectors, the cylindrical ferrules are rotationally fixed relative to the connector housing in which the ferrule is mounted but there is no alignment mechanism to rotationally align the ferrule end faces relative to each other as they are abutted. This practice is not sufficient for multi-fiber ferrules. In multi-fiber ferrules of the type in co-pending application Ser. No. 08/540,288 assigned to the assignee of the present application, all the fiber bores clearly cannot be on the center line of the ferrule, thus it can be appreciated that the relative rotational position of opposed end faces is now just as critical as the relative lateral position of the two end faces.
Ser. No. 08/540,288 discloses the use of one rib formed inside a sleeve in conjunction with a precision inner diameter of the sleeve to achieve rotational and lateral alignment of opposed end faces of two ferrules. This arrangement suffers from the drawback of having to form or machine a precision inner diameter of the sleeve and a precision outer diameter of the ferrule which is difficult over such large surface areas.
Additionally, a formed rib with a precision inner diameter is not as precise as the use of guide pins inserted in the end face of ferrules as with MT type ferrules and MTP type connector which use MT ferrules as disclosed in U.S. Pat. No. 5,214,730 to Nagasawa. The use of two guide pins achieves precise rotational as well as lateral alignment because the two guide pins span the interface of the two opposed end faces into guide pin holes on the end faces. The guide pin holes in the end face of the ferrules are located very precisely relative to the fiber array also on the end face of the ferrule.
While the use of guide pin holes and guide pins has proven to align opposing ferrules very precisely, they are extremely tedious and troublesome to use. Initial insertion of the pins into the ferrule faces is painstaking and pins commonly fall out of the ferrules. The drawbacks of the guide pins are heightened even further in the connector and adapter application because the second connector to be inserted is inserted blind and a guide pin and guide pin hole may not line up due to slight variations in adapter and connector dimensions from part to part. Also, connectors are typically connected and disconnected frequently and guide pins may fall out. Another concern with guide pins is that a pair of connectors may be mated with less than both guide pins due to craft inadvertence or lack of training and the fibers would most likely not be aligned.
Yet another concern with guide pins is whether to always have one guide pin per one connector or have two guide pins in half of the connectors and none in the other half. With either option there is potential for guide pins to be transferred from one connector to the other when the connectors are disconnected. This renders that connector out of conformance with whatever guide pin scheme has been adopted. Moreover, in some applications, one of the connectors remains in the adapter and the other side of the adapter receives different connectors. The adapter acts as a shroud to the stationary protector making it impractical to see the status of the guide pins on its end face. Another drawback is the cleaning of the connector end faces. With guide pins in the connector, they must be removed before the end face can be properly cleaned.
Therefore a need exists for a connector and adapter arrangement which takes advantage of the preciseness of the guide pins' rotational and lateral alignment that is so critical with ferrules that have more than one fiber yet eliminates the various drawbacks associated with guide pins.